1. Field of the Invention
The invention is directed to an arrangement for preventing the introduction of thread into a bobbin thread tensioning device during a sewing operation and providing for the introduction of thread into such device when a bobbin winding operation is to be performed.
2. Description of the Prior Art
It is well known to provide a lockstitch sewing machine with bobbin winding mechanism as shown, for example, in U.S. Pat. No. 3,693,566 of The Singer Company issued Sept. 26, 1972. Such mechanism has been designed to provide for the introduction of needle thread by way of a thread guiding finger into a bobbin case thread tensioning device when a bobbin winding operation is to be performed, but to prevent needle thread carried by the looptaker of the machine from entering the tensioning device during sewing operations. However, in order to have the machine so perform, manufacturing tolerances at the location of the bobbin case and the tensioning device, where thread was to be introduced to the device for bobbin winding but prevented from entering during sewing operations, had to be prescribed within narrow limits. Adherence to such tolerances materially added to the cost of producing a machine. Further, even in a machine built to satisfy such dimensional tolerances, it sometimes happened that thread would fail to enter the bobbin case tensioning device when the machine was instructed to initiate a bobbin winding operation.
It is a prime object of the present invention to provide an improved arrangement effective to reliably control the movement of thread into and over a bobbin case tensioning device as required for bobbin winding and sewing respectively, without the need for an adherence to tight dimensional tolerances during the manufacture of the bobbin case or tensioning device.
Other objects and advantages of the invention will become apparent during a reading of the specification taken in connection with the accompanying drawings.